Among the many scientific breakthroughs developed as World War II loomed was the fluxgate magnetometer, which detects and measures magnetic intensities in its immediate area.

The Navy saw an immediate application for the device, testing it on the water and in aircraft to see if it would detect submarines. It worked, and the equipment contributed to the sinking of an untold number of German U-boats and helped reopen the straits of Gibraltar to Allied shipping.

The inventor of the fluxgate magnetometer was Victor Vacquier Sr., a Russian-born immigrant of French extraction. Mr. Vacquier died of pneumonia Jan. 11 at a La Jolla nursing facility. He was 101.

Mr. Vacquier came to San Diego in 1957 as part of the early faculty at the Scripps Institution of Oceanography.

Mr. Vacquier's work at Scripps in the Pacific Ocean helped confirm the theory of plate tectonics, the idea that portions of the Earth's crust have moved and that the continents once fit together as a single land mass.

“He was part of a number of people at Scripps in the late '50s and '60s who really had an excitement about going to sea,” said John Sclater, a fellow geophysicist. “They made it really fun for the people they mentored. They gave the individual scientists a lot of responsibility.”

Mr. Vacquier's attitude, Sclater said, could be summed up as, “Where do we go to next?”

Mr. Vacquier's father was a physician in czarist Russia and the future scientist was born in St. Petersburg in 1907. In 1920, after the Russian Revolution, smugglers assisted the family in fleeing to Finland, crossing a frozen gulf in two horse-drawn sleighs and walking the final six kilometers, according to the account passed down to Mr. Vacquier's son, Victor D. Vacquier.

From there the family returned to France, and Mr. Vacquier's mother, Tatiana, used some diplomatic connections to get herself and young Victor sent to Madison, Wis. The boy's European education was rigorous enough to qualify for admission to the University of Wisconsin, where he earned bachelor's and master's degrees by age 19.

His first work after college was at the Gulf Research & Development Co. in Pittsburgh, where he discovered the principle for the fluxgate magnetometer. The younger Vacquier said his father – wearing a Navy uniform without rank or insignia – was sent on missions off the carrier Block Island with the magnetic gear to detect German submarines and assist in efforts to sink them.

When the war ended, Mr. Vacquier helped improve the design of navigational equipment called gyrocompasses for Sperry Gyroscope in Great Neck, N.Y. The Mark 19 and Mark 23 gyrocompasses were standard equipment on Navy ships until the introduction of satellite navigation.

In 1953, Mr. Vacquier went to the New Mexico Institute of Mining and Technology for his first “pure research” position.

He was drawn to the Scripps Institution in 1957 by UCSD founder Roger Revelle. Mr. Vacquier's magnetometer was redesigned to be towed from a ship, and he used it to perform magnetic surveys of the ocean floor.